Printed circuit boards for electronics applications typically have leads to which electronic components, such as resistors, capacitors, integrated circuits, etc., are mounted to form a conductive coupling therebetween. The leads typically are in the form of conductive pads for surface-mount components and in the form of conductive through-holes for through-hole components.
The through-holes are in the form of orifices extending through the board; the internal walls that define the orifices are coated with an electrically conductive material. Pins on an electronic component are then inserted into the orifices and solder applied to physically bond the component to the board and to form a conductive link between the component and conductive pathways on the printed circuit board.
The solder is commonly applied in a molten form using a wave-soldering apparatus comprising a nozzle through which the molten solder is pumped. The molten solder flows out of the nozzle in the form of a wave, and a conveyor passes a printed circuit board across the molten-solder wave from an upstream side to a downstream side of the nozzle to allow the molten solder to contact the underside of the printed circuit board and to penetrate into the through-holes in the board. Further details of wave soldering apparatus are provided in U.S. Pat. Nos. 5,228,615 and 5,240,169, both of which are incorporated by reference herein in their entirety.
A hot-gas knife is positioned on the downstream side of the nozzle, relative to the path of the conveyor. A hot-gas knife is used to direct hot air against the underside of the printed circuit board to remove unwanted solder to prevent electrical shorting due to solder bridging (i.e., the formation of a conductive link due to misplaced solder) between conductive elements on the board.